Support, by in vitro evaluation, the process of selection of chemical candidates for carcinogenicity testing by the National Toxicology Program as well as other aspects of intramural activities in carcinogenesis research. This contract will test up to 75 compounds yearly in five strains of the Salmonella/Typhimurium Assay with and without S-9 metabolic activation. Up to 25 compounds may be retested in the event that the initial results are equivocal. Compounds will be procured and supplied by a chemical repository contract also directed by the Division of Cancer Cause and Prevention. Results will be delivered in a brief tabular and narrative form and a completed computer input data form supplied by the government.